Michael b



Oct. 15, 1929. M. B. STAZAK TELEPHONE SYSTEM Filed June 18, 1926 2 Sheets-Sheet 1 j 22/517701? HUME/55F Oct. 15, 1929. m. a STAZAK 1,732,034

TELEPHONE 5Y3? Filed June 18, 1926 2 Shoots-Sheet 2 Patented Oct. 15, 1929 MICHAEL B. STAZAK, OF CHICAGO, ILLINOIS, ASSIGNOR TO KELLOGG SWITOHBOAB-D 8a SUPPLY 00., OF CHICAGO, ILLINOIS, A CORPORATION OF ILLINOIS TELEPHONE SYSTEM Application filed June 18,

My invention relates to telephone systems and has to do more particularly with systems employing two Way trunk circuits for use between two exchanges as between a main exchange and a private branch exchange or two main exchanges and has for its object, a novel and improved system of the above type.

In systems of the above character a call originating at a main exchange will be answered by a so called A operator, who upon finding that the wanted line terminates at a distant exchange extends the connection over a trunk line leading to the distant exchange, and an object of my invention is the provision of busy signals associated with the trunk jacks of the trunk which terminate at the respective main exchanges and indicate the busy condi tion of the trunk.

A feature of my invention is the provision of a two way jack ended trunk circuit for interconnecting lines terminating at diflerent exchanges. The jacks of the trunk terminating at the respective exchanges have associated therewith busy lamps which are lighted when connection. is made with either end of the trunk to indicate the busy condition of the trunk.

Another feature of my invention is'the provision of means in the trunk circuit which con- 'trols the lighting of the busy signals and which signals remain lighted at the respective jack ended portions of the trunk until both plugs are removed from the jacks so as to prevent an operator from connecting to either end of the trunk while a plug remains in either jack.

For a more complete understanding of my invention reference may be had to the accompanying drawing which comprises Fig. 1 and Fig. 2, and by placing Fig. 2 to the rightof Fig. l the figures illustrate apparatus for connecting a calling subscriber A terminating at the exchange B in Fig. 1 with a called subscriber E terminating at the exchange D illustrated in Fig. 2.

Referring now more in detail to the apparatus illustrated, the substation A of Fig. 1 terminates at the exchange C in a line circuit L comprising a line relay LR, line lamp signal S,-eut off relay CO and an answering jack 1526. Serial No. 116,803

J. The called substation E ofFig. 2 terminates at the exchange D in a line circuit L comprising a line relay LR, line lamp signal S, cut off relay CO and an answering jack J. The cord circuit B of Fig. 1 located at the exchange C comprises an answering plug AP and a calling plug CP connected by the heavily marked conductors and having the condensers K and K interposed. Associated with the answering end of the cord circuit B is a sleeve relay SL and an answering supervisory relay AS which relays control the lighting of the answering supervisory lamp AL. A listening key LK is also associated with the answering end of the cord B, and when actuated connects the operators set 0 to the cord conductors of the cord B. The calling end of the cord circuit B comprises a sleeve relay SL and a calling supervisory relay CS which relays control the lighting of the calling supervisory lamp CD. The cord circuit B is adapted to complete connections between local calling and called subscribers terminating at the exchange C and through the medium of a ringing key RK associated with the calling end of the cord B ringing current from the generator G, connected'when the ringing key RK is actuated, signals the local called line. The cord B is also used for extending a connection from a subscriber at the local substation A terminating at the exchange C over the trunk T to a substation E terminating at the exchange D, or for completing a call initiated by a subscriber at the exchange D through the trunk T to a called subscriber at the exchange C. V

The trunk circuit T terminates in a trunk jack TJ which is multiplied in the difierent operators positions at the exchange C and into a trunk jack TJ which is multiplied in Associated with the the different operators positions at the extoo D, is a sleeve relay SL a line relay LE a busy signal control relay BCR and a line signal cut off relay LCR.

The operators cord circuit B at the exchange D comprises an answering plug AP and a calling plug CP connected by the heavily marked conductors and having the condensers K and K interposed. A sleeve relay SL and an answering supervisory relay AS' are associated with the answering end of the cord B and control the lighting of the answering supervisory lamp AL. A listening key LK is also associated with the answering end of the cord B and when actuated connects the operators sets 0 to the cord conductors of the cord B.

The calling end of the cord B comprises a sleeve relay SL and a calling supervisory relay CS, which relays control the lighting of the calling supervisory lamp CL. The cord B is adapted to complete connections between local calling and called subscribers terminating at the exchange D and through the medium of a ringing key BK associated with the calling end of the cord B ringing current from the generator G is connected when the ringing key BK is actuated, to signal the local called line. The cord B is also used for extending a connection from a substation as E terminating at the exchange D over the trunk T to a substation as A at the exchange C or for completing a call initiated by a subscriber at the exchange C through the medium of the trunk T to a called substation at the exchange D.

Having described in general the apparatus employed in the preferred embodiment of my invention as illustrated in Figs. 1 and 2, I will now describe in detail the operation of the apparatus in extending a connection from a calling subscriber to a called subscriber.

Assuming now that the subscriber at the substation A in the exchange C initiates a call, the removal of the receiver at the substation establishes an energizing circuit for the line relay LR of line circuit L traced from battery through the line relay LR, normal contact 2 of cut off relay CC through the closed contacts of the substation switch hook back to ground at normal contact 8 of cut off relay CO. Line relay LR upon energization closes its normal contact 4, and closes a circuit through the line signal S traced from battery through the signal S to ground at alternate contact 4 ot the line relay LR. The operator noting the lighted line signal S inserts the answering plug AP of the cord circuit B into the J of the calling line thus closing a series energizing circuit of the cut off relay C0 of the line cir cuit L and the sleeve relay SL of the cord circuit B, traced from battery, through the winding of the sleeve relay SL, conductor 5, 52195 '1 2 :ontacts of the connected plug AP and jack J to ground through the windin of the cut off relay CO. Cut off relay CC upon energization opens its normal contacts 2 and 3 and disconnects the line relay LR from the subscribers line and completes the con nection between the substation A and the cord conductors of cord circuit B. An energizing circuit is now closed for the answering supervisory relay AS of the cord B traced from battery through the lower winding of the relay AS, the ring contacts of the connected plug AP and ack J, alternate contact 2 of the cut off relay CO, through the substation A, back through alternate contact 3 of cut off relay CO, tip contacts of the connected jack J and plug AP to ground through the upper winding of the relay AS. The relay AS upon energization opens its normal contact 6 to prevent the premature li hting of the answering supervisory lamp XL.

The operator now actuates the listening key LK to connect her operators set 0 to the cord circuit B and inquiries the wants of the calling subscriber at substation A. Upon learning that the calling subscriber desires connection with a subscriber at substation E at the exchange D the operator inserts calling plug CP of the cord B in the trunk jack TJ of trunk circuit T which leads to the exchange D. Upon the insertion of plug CP into the trunk jack TJ an energizing circuit is closed for the sleeve relay SL of the trunk T and sleeve relay SL of the cord circuit B traced from battery through the winding of the sleeve relay SL, conductor 7, sleeve contacts of the connected plug CP and trunk jack TJ to ground through the winding of the sleeve relay SL of the trunk T. The sleeve relay SL of cord B upon energization closes its alternate contact'8 and establishesa circuit for the calling supervisory lamp CL of cord B traced from battery through the lamp CL, normal contact 9 of the calling supervisory relay OS to ground at alternate contact 8 of sleeve relay SL. The calling supervisory lamp CL is lighted over this circuit and remains lighted until the operator at the exchange D answers the call to notify the operator at the exchange C that the operator at the exchange D has answered the call that is extended to that exchange.

The sleeve relay SL of the trunk D upon energization closes its alternate contacts 10, 11 and 12 establishing an energizing circuit for the line relay LR of the trunk Tand the busy signal control relay BCR traced from battery, through the lower winding of the relay LE conductor 13, alternate contact 12 of relay SL through the lower winding 14 of the busy signal control relay BCR, conductor 15, alternate contact 11 of relay SL conductor 16, alternate contact 10 of relay SL conductor 17 to ground through the upper winding of the line relay LE The closing of alternate contact 11 of the sleeve relay SL places a shunt about the upper high resistance winding 18 of the relay BCR and the circuit just traced through the lower winding 14 of the relay BCR permits the line relay LR and the relay BCR to energize. The closing of alternate contact 19 of the relay BCR establishes a circuit for the busy lamps associated with the trunk TJ which appear before the different operators positions of the exchange C, this circuit being traced from battery through the lamps BL, conductor 20 to ground at alternate contact 19 of relay BCE and the lighting of the busy lamps BL which appear before the different operators posiions apprise the operators of exchange C of the busy condition of the trunk T with which the jack TJ is associated. The closing of alternate contact 21 of the relay LE closes the circuit for the line signal control relay LCR traced from battery, through the Winding of the relay LCR, conductor 22, alternate contact 21 of the relay LE to ground at alternate contact 19 of the relay BCR. Relay LCR upon energizing opens its normal contact 23 to prevent the lighting of the lamp signal LS and the closing of its alternate contact 23 establishes a locking circuit for itself traced from battery, through the winding of the relay LCR, alternate contact 23, conductor 24 to ground at alternate contact 19 of the relay BCR.

The insertion of the calling plug CP of the cord B into the trunk jack TJ of the trunk 'P also establishes an energizing circuit for the relay BCR associated with the trunk jack TJ o1 the trunk T terminating at the eX- change D, traced from battery through the lower Winding of the calling supervisory relay CS of the cord B at the exchange C, nor mal contact 25 of the ringing key BK, ring contacts of the connected plug CP of the trunk jack TJ, conductor 26, normal contact 27 of the sleeve relay SL of the trunk T, condoctor 28 through the high and low resistance windings 29 and 30 of. the relay BCR, conductor 31, normal contact 32 of the sleeve relay SL conductor 33, tip contacts of the jack TJ and plug CP, normal contact 34 of the ringing key RK to ground through the upper winding of the calling supervisory relay CS of the cord B. Due to the high resistance winding 29 of the relay BCR the relay GS of the cord B fails to energize thus permitting calling supervisory lamp CL to remain lighted. The closing of alternate contact 35 of the relay BCR establishes a circuit for the busy signal lamps BL associated with the trunk jack TJ appearing at the ditt'erent operators positions at the exchange D traced from battery through the said lamps, conductor 36 to ground at alternate contact 33 ct relay BCR. The busy signal lamps BL associated with the trunk jacks TJ which appear at the different operators positions at the exchange D are lighted and apprise the operators that the trunk T has been placed in use and prevent an operator at the exchange D from using this trunk T for extending an outgoing connection from the exchange D.

The closing or" alternate contact 35 of relay BCR also establishes an energizing circuit for the line signal LS associated with the trunk jack TJ which terminates at the exchange D, traced from battery through the lamp signal LS, conductor 37, normal contact 38 ot the relay LCR of trunk T, conductor 39 to ground at alternate contact 35 of the relay BCR.

The line lamp signal LS lighting, apprises the operator at the exchange D at whose position the trunk jack Til of the trunk T terminatest that a call has been extended over the trunk T to her position. The operator now inserts the answering plug AP of the cord circuit ll at the exchange D into the trunk jack Ti and closes a circuit traced from battery, through the Winding ol the sleeve relay till or: the cord c rcuit B, conductor 40, sleeve contacts of the connected plug AP and trunk jack Til to ground, through the winding of the sleeve relay til ot' the trunk T. The sleeve relay SL oi the trunk T upon encrgization closes its alternate contacts 4i, and 13 establishing an energizing circuit for the relay Lil" ot' the trunk T traced from battery, through the lower winding of the relay LR, conductor -14, alternate contact 43 of relay SL conductor 31, through the lower winding 30 of the relay RC3, conductor alternate contact 4-2 at the relay E5 1", con-- ductor 28, alternate contact ll of relay SD. and conductor 40 to ground through the upper winding of relay LR. The closing of alternate contact of the relay SL places a shunt about the upper high resistance winding 29 of the relay BUR and the relay Till is energized over the circuit just traced and relay BUR also remains energized over this circuit. The relay LR upon enei 'zatiou closes its alternate contact 47 thus es -hlislr ing an energizing circuit for the relay Lilli". traced from battery. through the winding of the relay LCR, conductor 18, alternate contact :7 of relay Lil to ground at alternate contact 35 of the relay lltllt'. The relay LCR upon ei'iergization opens its normal con-- tact 38 to ell'ace the signal LS and the (losing 01' alternate contact 38 ot relay litllt' estal'ilishes a locking circuit for itself traced from battery through the winding of the relay LCR its alternate contact 38, conductor 39 to ground at alternate contact 35 of relay DCR' A circuit for the answering SlllllVlsoi'X' relay A53 of the cord B at the exchange l) also established, traced from battery. through the lower winding of the relay A5 1, the ring contacts of the connected plug AP. trunk jack TJ, the tip contacts of the trunk jack TJ and calling plug CP of cord circuit B at the exchange C, normal contact 34 of the ringing key RK to ground, through the upper Winding of the relay CS of the cord circuit B at the exchange C. A circuit also extends from battery through the lower winding of the supervisory relay CS of the cord l3, through normal contact of ringing key BK, ring contacts of connected plug Cl trunk jack TJ, tip contacts of trunk jack TJ and the answering plug Al of the cord circuit ll, at the exchange 1) to ground through the upper Winding of the relay AS of the cord circuit B.

Upon the energization of the sleeve relay SL ot the trunk T its normal contacts 27 and 32 are opened and the initial circuit which extended through the relay CS of cord circuit ll at the exchange l is opened to disconnect the high resistance winding 2!) of relay BCR and an energizing circuit is now established tor the relay (S of the cord circ it B at the exchange C over the (ircuit as just descrbed and permits the relay CS ot the cord l to cum and the opening of its normal contact 9 enaces the s lfll CS of the cord 1} and apprises the c ratoi' of the cord circuit 1 at the crechangc C that the operator at the exchange D has inserted an answering plug Al into the trunk jack TJ ot' the trunk circuit. T. The sleeve relay SL ot the cord circuit ll at the exchange D is energized when the plug AP is inserted into the trunk jack TJ and as the relay AC is energized over the circuit just traced the opening of its normal contact prevents the premature lighting of the answering supervisory lamp AL.

The operator of the cord circuit 13 at the exchange 1) now actuates her listening key Lli to connect her operators set 0 to the cord conductors of the cord circuit B and converse-s with the operator of the cord circuit B at the exchange C or the subscriber at the calling substation A as the may be, and receives the number of the substation wanted. Upon being informed that it is the called substation E but is wanted the operate inserts the calling plug Cl" into the jack J of the called line which estahlishes a series energizing circuit tor the sleeve relay SL ot the cord circuit l3 and cut oil relay Ci) of the line circuit L, raced from battery through the winding of the relay SL ccnductor 51. sleeve contacts of the connected plug Cl and jack J to ground through the winding of the cut oii re ay CO ot the line circuit L. Cut oil relay CO upon energization eisconnects the line relay LR from the line of the called subscriber and connects the line of the called subscriber to the strands of the cord circuit B through its alternate contacts 52 and 53. The sleeve relay SL upon energization closes its alternate contact 54 establishing a circuit for the calling supervisory lamp CL, traced from battery, through the lamp CL, normal contact 55 of the calling supervisory relay CS to ground at alternate contact 5-1 of the relay SL said lamp remaining ii ghted until the called subscriber at substation E answers. The operator now actuates the ringing key BK of the cord circuit B to connect ringing current of genorator G to the called line. Ringing current may now be traced from the generator it through alternate contact 56 of ringing key RK, tip contacts of the connected plug Cl and jack J, alternate contact 52 of cut oil relay CO through the condenser and call bell of the called substation E back through alternate contact 53 of relay CO, ring contacs of the jack J and plug CF to ground at alternate contact 57 of ringing key RK.

The subscriber at the called substation E in response to the signal, removes the receiver from the switchhook thereby establishing a ircu t for the calling supervisory relay CS traced from battery, through the lower windot the relay CS, normal contact 57 ot ing LIP) RK, ring contacts of connected 11g Cl and jack J. alternate contact 53 oi relay CO, the now closed contacts of the sulaztation switchhook back through altercontact 52 of relay CO, tip contacts of the connected plug CP and jack J, normal contact 56 of the ringing key RK to ground through the upper winding of the relay CS. The relay CS is energized over the ircuit and opens its normal contact 55 to ctiace the signal CS thus apprising the operator of the cord circuit B that the called subscriber of the substation E has responded. The calling subscriber of substation A at the exchange C and the called subscriber at the ion E, at the exchange D are now in conversational circuit, the talking circuit beiug traced over the heavily marked conductors.

From the above description it is readily apparent that the instant that the calling plug Cl ot the cord B at the exchange C is inserted into the trunk jack TJ ot the trunk T the busy lamp signals BL associated with the jack TJ and the busy lamp signals BL assoc'ated with the jack TJ are lighted to prevent the operators of either exchange C or D from seizing this trunk T. The lamps BL and BL remain in this lighted condition until the plugs CP ot the cord B at the exchange C, and AP of the cord B at the exchange D are removed from the respective jacks T J and TJ as will be more fully hereinafter described.

Assuming noW that conversation has terminated. the calling subscriber at substation A upon replacing his receiver opens the circuit of the answering supervisory relay AS of the cord circuit B at the exchange C at the switchhook contacts and thereby allows the same to deenergize. The answering su pervisory relay AS upon deenergizing, closes a circuit for the answering supervisory lamp AL traced from battery, through the lamp AL, normal contact ('3 of relay AS to ground at alternate contact (50 of the sleeve relay SL. The called subscriber at substation E at the excl'iauge D upon replacing his receiver opens the circuit of the calling); supervisory relay CS ot' the cord circuit B at the exchange D at the switchhook contacts of the substation thereby allowing relay CS to deenergize.

The calling supervisory relay CS upon deenergizing, closes a circuit for the calling supervisory signal CL of cord B from battery, through the lamp CL, normal contact 55 of relay CS to ground at alternate contact 54 of sleeve relay SL The two lighted supervisory signals AL and CL of the cord circuits B and B at the respective exchanges C and D apprise the operators associated with the respective cords B and B that the calling and called subscribers have replaced their receivers upon their respective switchhooks.

The operators associated with the cord circuit B and B at the respective exchanges C and D noting the two lighted signals AL and CL remove the respective plugs AP and CP of the cord B from the jacks J and TJ and the respective plugs AP and CP of the cord B from the jacks TJ and J. The removal of the plug AP from the jack J opens the series circuit of the cut oil relay C0 of line circuit L and the sleeve relay SL of the cord B. The relay CO restoring again places the line relay LR under the control of the substation A and the restoration of sleeve relay SL etfaces the supervisory signal AL. The removal of the plugs CP and AP by the opera tors associated with the cords B and B at the respective exchanges C and D from the jacks TJ and TJ of the trunk T allows the relays SL and SL of the trunk T to restore. The relay SL upon deenergization opens the circuits of the relays BCE and LR assoeluted with the trunk jack T'J at contacts 10, 11 and 12 of relay SL and the deenergization of relay SL associated with the jack TJ opens the circuit of relays BCR and LE at the contacts 41, 42 and 43 of the sleeve relay SL The relay BCR upon deenergizing opens the locking circuit of the relay LCR at its alternate contact 19, and the opening of its contact 19 also opens the circuit of the busy lamps BL associated with the trunk jack TJ. The relay BCR upon deenergizing opens the locking circuit of the relay LCR at its alternate contact 35 and the opening of this contact also opens the circuit of the busy lamps BL associated with the trunk TJ. The busy lamps BL and BL associated with the trunk jacks TJ and T J terminating at the respective exchanges are effaced as just described and apprise the operators at the exchanges C and D that the plugs have been removed from the jacks TJ and TJ of the trunk T and the trunk is now available for use in interconnecting the exchanges C and D. The withdrawal of the plug CP from the trunk jack TJ allows relay CS and relay SL ot' the cord B at exchange C to restore and the withdrawal of the plug AP from the trunk jack TJ allows relay SL and relay AS of the cord B to restore. The withdrawal of the plug CP from the ack J at the exchange D allows relays SL of the cord B and the cut off relay C0 of the line circuit L associated with the called substation E to restore. Relay SL restoring elfaces the supervisory signal CL and the restoring of cut off relay CO again places the line relay LR under the control of the subscriber at the substation E. The apparatus at the exchanges C and D and the trunk T used for interconnecting the subscribers A and E is now at normal and available for establishing other connections.

Assuming that the operator of the cord B at the exchange C is the first to remove the plugs AP and CP from the jacks J and TJ after receiving the disconnect signal by the lighting of the supervisory signal AL, the removal of the plug AP from the jack J of the calling line A opens the series energizing circuit of the cut off relay CO and the sleeve relay SL as before described. The removal of the plug CP of the cord B from the jack TJ of the trunk T opens the series circuit of relay SL of the cord C and the relay SL of the trunk T and also allows the relay CS of the cord B to deenergize. The relay SL of the trunk T upon deenergizing opens its alternate contacts 10, 11 and 12 to open the energizing circuits of the relays BCE and LE and assuming further that the operator of the cord B is busy attending to other local connections and has as yet not removed the plug AP of the connected cord B from the jack TJ, the relays BCR, LE LCR and SL remain energized. As just pointed out when the plug CP was removed from the trunk jack TJ relay SL of the trunk T deenergized and opened the energizing circuit of relays BCR and LE but as the plug AP of the cord B at the exchange D is still in the trunk TJ a substitute energizing circuit for relay BCR- is closed. This substitute energizing circuit for relay BCR is traced from battery through the lower winding of relay AS of the cord B at the exchange D, ring contacts of the connected plug AP and jack TJ, conductor 61, make before break contact 62 of relay SL (which is at normal as just described) through the high and low windings 18 and 14 of relay BCR, make before break contact 63 of relay SL conductor 64, tip contacts of the connected jack TJ and plug AP to ground through the upper winding of relay AS and relay BCR remains in its energized condition independent of the relay SL and relay L11 Alternate contact 19 of relay BCR maintains the busy lamps BL associated with the trunk jack TJ lighted to apprise the operators of the exchange C that trunk T is still in a busy condition and thus prevent an operator of the exchange D from using this trunk T. The relay LCR also remains in its locked position to ground at alternate contact 19 of relay BCR and prevents the lighting of the signal LS associated with the trunk jack TJ. The circuit just traced through the relay AS of the cord B caused relay AS to deenergize due to the high resistance winding 18 of relay BCR of the trunk T and the relay AS deenergizing, its normal contact 50 is closed to close a circuit for the supervisory signal AL of the cord B to ground at alternate contact 65 of the relay SL and the lighting of this supervisory lamp AL apprises the operator of the cord B at exchange D that the operator at the exchange C has withdrawn the plug CP from the jack TJ. The busy lamps BL associated with the trunk jack TJ at the exchange D remain lighted and also prevent any operator at the exchange D from connecting with any multiple of the trunk jack TJ appearing at their positions.

When the operator of the cord B withdraws the plug AP from the jack TJ the circuit for relay BCR associated with the jack TJ terminating at the exchange C and the relay AS of the cord B at exchange D is opened which allows relay BCE to deenergize and the opening of its alternate contact 19 efi'aces the busy lamps BL associated with the ack T J and also opens the locking circuit of the relay LCR which restores to normal. The removal of the plug AP from the jack TJ also opens the energizing circuit for the relay SL of the trunk T and the relay SL of the cord B. The relay SL upon deenergizing, its alternate contacts A1, 42 and 43 are opened, to open the energizing circuit of the relays LE and 13GB and the opening of alternate contact 35 of relay BCR etf aces the busy signal lamps BL associated with the jack TJ and also opens the locking circuit of relay LCR which restores. The relay SL of the cord B upon deenergizing elfaces the supervisory signal AL and the removal of the plug CP of the cord C allows relays SL and CO to restore as before described.

Should the operator at the exchange D be the first to disconnect the plugs AP and CP from the jacks TJ and J the removal of the plug AP from the jack TJ opens the energizing circuit for the relay SL of the trunk T and the relay SL of the cord B. The relay SL upon deenergizing its alternate contacts 41, 4:2 and A3 are opened to open the energizing circuit for the relays LB and BCR but as the plug CP of the cord B at the exchange C is still in the jack TJ of the trunk T a substitute energizing circuit is thus established for the relay BCR, traced from battery through the lower winding of relay CS of the cord B at the exchange C, normal contact 25 of the ringing key BK, ring contacts of the connected plug CP and jack TJ, conductor 26, make before break contact 27 of the relay SL through the high and low resistance windings Q9 and 30 of relay BCR, make before break contact 32 of relay SL conductor 33, tip contacts of the jack TJ and plug CP, normal contact 34 of ringing key BK to ground through the upper winding of relay CS. Relay BCR remains energized over this circuit and the busy lamps BL associated with the jack TJ remain lighted and the locking circuit for this relay LCR is also maintained at the alternate contact 35 of the relay BCR to prevent the lighting of the signal LS. The busy lamps BL associated with the trunk TJ also remain lighted as long as the plug CP remains in the trunk jack TJ and these busy lamps BL and BL associated with jacks TJ and TJ of the trunk T remain lighted and prevent any operator at either exchange from seizing any of the multiples of the jacks TJ and TJ while a plug remains in either jack. The relay CS of the cord B fails to energize by reason of the high resistance winding 29 of relay BCR and the supervisory lamp CL is lighted for the same purposes as described in connection with the signal AL of the cord B at the exchange D. \Vhen the operator at the exchange C withdraws the plug CP from the jack TJ of the trunk T relay BCR is deenergized and the opening of its alternate contact 35 etfaces the busy lamp signals BL and also opens the locking circuit of relay LCR. The withdrawal of the plug CP from the jack TJ also allows relay SL to deenergize and the opening of its alternate contacts 10, 11 and 12 opens the energizing circuit for relays BCR and LR The opening of alternate contact 19 of relay BCR opens the circuit for the busy lamps BL which are etfaeed and the opening of contact 19 also opens the locking circuit of the relay LCR. The disconnection of the plug AP from the jack J of the calling line brings about the restoration of relays CO and SL as is readily apparent from the previous description.

Assuming that the subscriber at the substa tion E which terminates at the exchange D wishes to converse with the subscriber at the substation A terminating at the exchange C, the removal of the receiver at E closes a circuit for the line signal S, and the operator in response to the signal inserts the answering plug AP of the cord B into the jack J of the line E which closes a circuit for relay SL of the cord B and cut off relay CO of line circuit L. Relay CO opens the circuit of relay LR to ellace the signal S and relay AS of B is energized over the line and relays AS and relay SL prevent the premature lighting of the supervisory lamp All. The operator of cord B now actuates her listening key LK and converses with the subscriber at E and having been informed that it is the subscriber A at the exchange C that is wanted the operator inserts the calla g t Y GP of cord B into the trunk jack To" f in trunk T which extends to the exchange C This insertion of the plug Cl closes a so. Ies circuit for the relay SL of the cord ll and the relay SL of the trunk T and the relay SL of the cord B closes a circuit for the supervisory lainp CL to gmund at alternate contact 54 of relay SL The relay SL of the trunk T upon energization closes its alternate contacts 4-1, 42 and 4310 establish an energizing circuit for the relays LE and BCR traced from battery through the lUY-ZOI winding of relay LE conductor 44, alternate contact 43 of relay SR conductor 81, w ling of relay BCR. conductor 45, alternate contact 42 of relay SL conductor 28 alternate contact 41 of relay SL conductor ii) to ground through the upper winding of relay LE The relay LE is operated orer this circuit because of the shunt placed aroun d the high resistance winding 29 of relay Bth at alternate contact 42 of relay SL Relay BCR upon energizing closes its alternate contact to close a circuit for the busy lamps BL which appear at the operators positions at the exchange D and the lamps Bil are lighted to apprise the operators at change D of the busy condition ot the T and thus prevent any operator from i. g this trunk T which is now in use. The (bl-u ing of alternate contact 47 of relay L 2 closes a circuit or the relay LCR to at alternate contact 35 of relay BC? an closing of alternate contact 38 of r: y Lt closes a locking circuit for itself, and ti 0 opening of normal contact 3 prevents t: lighting of the signal LS. \Vhen th ;lll GP was inserted into the jack Til a iifl'l'. for the relay BCR associated with the TJ of the trunk T terminating at th change C is also established traced from tery through the lower winding of rela C l of the cord B, ring contacts of the di 7 er.

and jack TJ. conductor 61, normal contact 62 of relay SL of the trunk 'l, the hi' l: and

low resistance windings 18 and 1 ot relay BCR normal contact 63 of relay Si ductor 6-1, tip contacts of the jack plug CF to ground through the uppe ing of relay CS. Relay BCR is en over this circuit, and the closing of it nate contact 19 closes a circuit for tl lan'ips BL assoiatcd vith the inul iples of the jack TJ of the trunk T which meat at the different operators positions at the 0'?- change C. The lamps BL which appear at the operators positions at the exchange C are lighted and apprise the operators at exchange C of the busy condition of the trunk and thus prevent any operator from seizing this trunk T which is now in use. The closing of alternate contact 19 of relay BCR also closes a circuit for the line lanip signal LS traced from battery through the lamp LS, conductor 70, normal contact 23 of relay LC H cc-niluctor 24 to ground at alternate contact .19 of relay BCR. The lamp LS is lighted over this circuit and apprises the operator associated with the cord B at the exchange C that a call is awaiting her attention. The relay CS of the cord B at the exchange I) does not energize over the circuit traced for relay BCR due to the high resistance winding 18 of relay BCR and the relay CS remains at nor mal and a circuit for the supervisory signal CL is thus closed through its normal con tact to ground at alternate contact 54 of relay SL the said signal remaining lighted until the operator at exchange C answers the call extended to her position.

The operator at the exchange C not ing the lighted signal LS inserts tae answering plug AP of the cord circuit B into the jack TJ ot the trunl; T to close a series circuit tor relay SL ot the cord B and the relay SL oi the trunk T. The relay SL upon energizing closes its alternate contacts 10. 11 and 12 to establish an energizing circuit for relay Ll: traced from battery through the lower wind ing of relay LE conductor 13, alternate contact 12 of relay SL lower winding 13- ct relay BCR, conductor 15, alternate contact 11 of relay SL conductor 16, alternate contact 10 of relay SL conductor 1? to ground through the upper winding of relay LR Relay LR is energized ever this circuit b cause a shunt is placed about the high res t ance winding 18 of relay BCR at alternate contact 11 of relay SL Relay Btll is held energized over this circuit and the cl sing of alternate contact 21 of relay LR close a cir cuit for relay LCR to grouiul at alt rnate contact 19 of relay BCR. The relay LCR energizing, its normal contact 23 is opened to ctlace the line signal LS and the clo 1: of its alternate contact 23 closes a lock mg circuit for itself to alternate contact 19 oi relay BCR independent of the contact 21 of relay L11 The circuit through relay CH of the cord B at exchange D is interrupted at contacts 62 and 63 when the relay SL of trunk T energized but when the plug AP is inserted into the jack TJ a circuit for relay AS of cord B at exchange C and relav CS of cord B at exchange I) is closed as lzctorc described and the relays AS and CS operate over this circuit. Relay AS opera prevents the premature ligl'iting or the super visory signal AL and the operation of relay CS eiiaces the signal CL and notifies the operator of the cord B at exchange D that the operator at exchange C answered the call.

of the circuit t'rom this point is the same as previomly tltt-(l'il)ltl when co tion was established between the calling sul-si riber at A and the called subscribe at E. The d1 connection of the apparatus: atter the conve sation has been completed is the same and the functioning of the busy lamps BL and BL associated with the jacks T5 and i l of the trunk 'i is prr-icticaliy the same as hereinbetore described.

\Vhile I have illustrated the preferred cinbodimcnt of my invention it to be understood that I do not wish to h lim ted to the specific arrangement. as shown as changes and modifications will readily t themselves to those skilled in the art, and l t ieretore desire to cover all such char. es and modifications that come within the spirit and scope of the appended claims.

hat I claim as new and desire to secure by United States Letters Patent, is:

1. A telephone system comprising a two way trunk circuit provided with a pair of terminals extending between two operators switchboards, busy signals associated with each of said pair of terminals, cord circuits at said operators switchboards provided with connection terminals, means in said trunk circuit for operating said busy signals associated with said pair of tern'iinals when a connection is made with either of said pair of terminals by said connection terminals of said cords, and means for maintaining said signals operated during said connection.

2. In a teiephone system a two way trunk circuit provided with a pair of teri'i'iinals extending between a pair of operators switchboards, busy signals associated with each of said of terminals, operators cords at said switchboards provided with connection terminals, means associated with each of said terminals operated when a connection is made with either of said pair of terminals by a connection terminal of an operators cord ot said eperators switchboard to operate said busy signals, and means for maintaining said signals in an operated condition subsequent to the connection of another of said terminals.

3. In a telephone system a two way trunk circuit provii'led with a pair of terminals extending between operators switchboards. busy lamps associated with said pair of terminals, ope *ators cords at said switchboards provided with connection contacts, and control means for said busy lamps associated with each of said terminals actuated when a connection is made with either of said terminals by a connection contact of an operators cord of either operator of said operators switchboards, said means remaining actuated during said connection.

4. In a telephone system a two way trunk circuit provided with a pair of terminals terminating respectively at operators switchboards. busy signals associated with said pair of terminals, control means for said busy signals in said two way trunk circuit and associated with each of said terminals, operators cords at said switchboards, connecting plugs associated with said cords at said operators switchboards adapted to be connected to said pair of terminals, said control means operating when one of said conuecting plugs is connected with either of said terminals to operate said busy signals to indicate the busy condition of said trunk, said signals remaining actuated during the entire connection of said plug and said terminal.

5. A telephone system including a two way trunk circuit provided with a pair of jack terminals extending between a pair of exchange switchboards, operators cords associated with said exchange switchboards, busy signal:-; associated with said pair of aek terminals, means associated with each of said jack terminals for controlling the operation of said signals, connecting means associated with an operators cord at one of Said exchanges for connection with a jack terminal of said trunk to operate means associated with said connected jack terminal to operate said signals associated with said connected jack terminal and affect m ans associated with the jack terminal terminating at said other exchange switchboard to operate the busy signals associated with the said jack terminal at said other exchange switchboard, said busy signals remaining actuated during the connection of said connecting means and said jack terminal.

6. A telephone system including a two way trunk circuit provided with a pair of jack terminals extending between a pair of eX- change switchboards, operators cords associated with said switchboards, busy signals associated with said pair of jack terminals, a relay associated with each of said jack terminals, tor controlling the operation of said busy sign als,connecti n g means associated with an operator s cord at one of said exchanges for connection with a jack terminal of said trunk to operate means in said trunk to effect the operation of the relay associated with said connected jack, said relay of said other jack terminal operating through means associated with the connecting means of said connected exchange cord, said relays operating to actuate said busy signals of said jack terminals of said trunk.

7. A telephone system including a two way trunk circuit provided Witha pair of jack terminals extending between a pair of exchange switchboards, busy signals associated with said pair of jack terminals, operators connecting cords associated with said switchboards, a relay associated with each of said jack terminals for controlling the operation of said busy signals, a connecting plug for one of said cords at one of said exchanges for connection with a jack terminal of said trunk, means in said trunk associated with said connected jack terminal operated by said connection to operate said relay of said connected jack terminal to actuate the busy signals associated with the said connected jack, the relay associated with jack terminal at the opposite end of said trunk operating through means in said connected cord to actuate the busy signals associated with the jack terminal at the opposite end of said trunk.

8. A two-way trunk circuit provided with jack terminals terminating at a pair oi exchanges, busy signals associated with said jack terminals, connecting cords for said exchanges terminating in connecting plugs adapted for connection with said jack terminals for interconnecting said exchang s through the medium of said trunk, means associated with each of said jack terminals operated when connection is made with each of said jack tern'iinals by the said plugs of said connecting cords at said exchanges to actuate said busy signals associated with the respective jack terminals, and a relay associated with each of said means remaining energized during the connection of both cords to the jack terminals or when either of said connecting cords is disconnected from its connected jack terminal of said trunk to maintain said busy signals actuated at all times during the connection of one of said cords and one of said jack terminals.

9. A two way trunk provided with jack terminals terminating at a pair of exchanges, busy signals associated with said jack terminals, connecting cords for said exchanges terminating in connecting plugs adapted for connection with said jack terminals for interconnecting said exchanges through said trunk, means associated with each of said jack terminals operated when connection is made with each of said jack terminals by the said plugs of said connecting cords at said exchanges to actuate said busy signals associated with the respective jack terminals, a relay for each of said means remaining energized when either one of said connecting cords is disconnected from its connected jack terminal, said relay associated with the connected end of said trunk remaining energized through its associated means and said other relay associated with said disconnected end remaining energized through means associated with said connected cord, said relays maintaining said busy signals actuated.

10. A telephone system including a two way trunk circuit ending in terminals at different exchanges, busy visualizing means associated with said terminals, operators cords at said exchanges and means associated with said cords for connecting to said trunk cir cuit, and automatic means including a pair of relays for maintaining said busy signalling means actuated so long as a connection exists with said trunk circuit.

11.. A telephone system including a two way trunk circuit ending in terminals upon switchboards, busy signalling means associated with said terminals, operators cords at said exchange and means associated with said cords for extending a connection to either end of said trunk circuit, and means including a pair oi relays for maintaining said busy signalling means in an operative condition so long as a connection exists with the said trunk circuit.

12. A telephone system including a two way trunk circuit extending between two exchanges, multiple terminals associated with each end ol said trunk circuit, busy signalling means associated with each of said terminals, operators cords at said exchanges and means associated with said cords for effect ing connection with said trunk circuit, and relay means for maintaining said busy signalling means operative so long as a connection exists with said trunk circuit.

Signed by me at Chicago, in the county of Cook and State of Illinois, this 15th day of June, 1926.

MICHAEL B. STVAZAK. 

